I agree with you, Affected. It's unique, I mean each peace of metal/rust. But I still think that you can learn basics from someone else. Why do you have to reinvent it each time? There is a base, which is pretty much the same for all rusty stuff.... at least I think so and nobody gives a damn shit to what I think, right?! Yoohoo! =)

and what's up with my damn signature?? it should be TWO lines!!
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Alex D. G.
http://www.alexdg.com

Kusanhagi, it seems there are few, if any good tutorials on those subjects, since usually the methods people use are pretty complex, and also involve heavy aribrush/dodge/burn usage.
So, if you ask me, (Which, of course, you didn't , the best thing you can do is study the things you want to replicate in PS. You can't just run a few filters and actions and get good images. You need to understand the properties of the materials. Study what happens to metal when it's corroded, if that's what you want to do.
I've found that corroded stuff can generally be divided into areas. There are dark spots, light spots, and a lot of random things like scratches and such. So study the materials. Try to think not how to make the effect straight off, but how to make selections for the different parts, the areas I spoke of. Selections are your friends.Once you make a selection, you can use that for a lot of things. Darkening, lightening, adding noise, just generally dividing the image into areas where you want different effects to appear...
Also, the drawing tools are your friends as well. For cracks, the smallest brush sizes are great. Nothing beats total control. Your best bet for making cracks would be to just draw them.

I'll post an image I made recently, of metallish stuff. It'll be in the 'art' forum.
(Don't want to take this thread over :P )